Very large, mobile vacuum units of the sort which are truck mounted have been known for some time. Generally, such units have amounted to very little more than over-sized vacuum cleaners of the sort found in the home or workshop. In other words, a collector box or tank of some sort is provided, having a snorkel or suction hose at one end, and an attachment to an air blowing unit at the other end. Crude filtering means are often provided, usually screens, bags or precipitators. Such units are generally only useful for dry material, such as heat or grain, dry limestone, catalytic materials, millscale, etc. When damp materials such as wet flue dust, wetted ore pellets and coal, slaked lime and so on are collected using industrial mobile vacuum units as known heretofore, the materials have tended to agglomerate or cake in the ducts and tubes, or within the collecting box or tank -- usually because of insufficient filtering or an inability to fluidize the material. In addition, dumping the material is sometimes difficult, especially where the tank or collector box cannot be tilted.
A very definite need exists for a mobile vacuum and pneumatic unit which may be used continuously to withdraw material -- wet or dry -- from one place and to discharge that material to another. If the material is in a cargo hold, a catch basin or other relatively inaccessible place, ordinary conveyors may not be usable. Heretofore, it has been known to use a single tank mobile vacuum unit of the usual type, and to collect material until the tank is full, stop the collecting operation and blow the tank to discharge the material therein in the designated place. However, such intermittent operation may not always be satisfactory; but an almost continuous operation where the off time is only as long as may be required to adjust a valve setting, can be acceptable.
The use of float valves to shut off or close a collector box or tank with respect to the vacuum source is well known. However, if the unit is to be adapted so as to accommodate wet or dry material, and of fine particulate size or lumpy material, suitable means should be provided to preclude inadvertent and unnecessary operation of the float valve because of its reaction to being contacted by material which is not at the effective shut-off height for that tank. Such means include suspended baffles within the tank; and as well, a primary knock-out screen -- a mechanical screen -- may be installed within the tank.
In view of all of the above drawbacks and shortcomings of the prior art devices, it has been suggested to provide a mobile vacuum and pneumatic unit having two tanks. Such a solution was, indeed, proposed in Young U.S. Pat. No. 3,424,501 dated Jan. 28, 1968. which disclosed a two-tank system. However, that system requires the use of both tanks because the first tank is a collector tank which operates at negative pressure, and the second tank is a filter backwash and conveyor tank which operates at positive pressure. Only a single air flow energizer is provided. (The patent also teaches that the use of a single tank, having intermittent operation thereof, may be provided.)
This invention, on the other hand, provides a mobile vacuum and pneumatic unit which may be used for collecting storing and discharging air conveyable materials of all sorts, and which consists of a mobile frame having a power source -- usually a truck body although a large towable float might be used for land operation, or a boat such as a tug or trawler might be used for water-based operation. Usually two tanks for collecting and storing the air conveyable materials are provided, and two separate air energizers or means for creating a vacuum are provided. Suitable valve arrangements are made so that at least one or more than one of the tanks may be selected for collecting and storing of material at one time, by communicating the selected tank or tanks through inlet valves thereof with an inlet port connected to an intake hose or snorkel, for example. Each of the tanks is provided with a float operated valve, and communicates through that valve to an exhaust header duct. The exhaust header duct communicates through air filtering and cleaning devices -- such as a venturi scrubber and a demister -- to a three-way valve which has an inlet and two outlets and means within the valve so that the inlet can be in communication with either or both of the two outlets. The two vacuum air energizers are connected respectively to each of the two outlets of the three-way valve; and the outlet of at least one of the air energizers is connected through yet a further valve so that it may exhaust either to the atmoshpere or communicate at a positive pressure back to any one or a plurality of the work tanks.
Thus, the present invention provides an apparatus which is mobile and self-contained, and which has vacuum and pneumatic operation. Any tank, even if it is in vacuum communication with an air energizer to pull a vacuum within that tank, may also be connected in pressure communication with the output of a blower so that the material within the tank may be fluidized if necessary; or the tank may be pressurized to expel the material in it.